IMHO it would be impossible to choose between them. In the short term it has to be OLOG because they do pay better at the moment. But in the long term, who knows ? Probably not even the bean counters.
I hear CHC are going to get really aggressive and try to put OLOG out of Nigeria, but some companies (eg Shell/ExxonMobil) won't touch them. My money is on OLOG. They seem to be going through a revamp and appear to have client loyalty.
Not authoritative, just my thoughts.
Cheers,
NEO